Field of the Invention
The present invention relates to a sheet feeding apparatus capable of mounting a sheet cassette in which paper sheets are stored.
Description of the Related Art
In a conventional printing apparatus such as a printer in which a paper sheet is fed from a sheet cassette storing sheets therein, the sheet is coated with ink, and thermal transfer is performed, various failures will occur if a draw-out of the sheet cassette is performed due to an erroneous operation or the like during operation after sheet feeding.
For example, when a sheet sandwiched by rollers is forcibly pulled out, there may occur troubles such as occurrence of jamming or breakage of the sheet. In particular, in a roll paper printer such as the one in which a roll-shaped sheet is pulled out and cut after performing photographic printing, the sheet remaining in the sheet cassette and a portion where the photographic printing process is being performed are connected with each other, even after the sheet feeding.
For this reason, if an attempt of forcibly drawing out the sheet cassette is made, the sheet is likely to be damaged, in most cases. In particular, in a printing apparatus such as the one in which a conveyance direction of the sheet and a loading direction of the sheet cassette intersect at right angles to each other, even a little positional deviation or inclination of the cassette exerts significant influence on a head at a conveyance destination of the sheet, and a conveyance path.
For example, even a small inclination at a sheet cassette unit causes positional deviations to be enlarged in a direction orthogonal to the conveyance path of the sheet, at a print head and at the conveyance path after the head, and the longer the distance is, the more significant the influence becomes. For this reason, the sheet is conveyed being greatly skewed to the print head. As a result, photographic print quality is deteriorated remarkably, and the sheet heavily bumps against a side surface of the conveyance path, thereby causing a serious jamming.
Reflecting on these problems, various mechanisms are discussed for locking the draw-out of the sheet cassette in order to prevent the sheet from being drawn out during the photographic printing or after the sheet feeding.
For example, in a printer such as the one in which photographic printing is performed while a print head and a platen are pressure contacted with each other, there is the one which includes an engagement member with the cassette so as to be integral with or to interlock with a driving side of either the print head or the platen. Generally there is employed a method such as the one in which the engagement member is engaged with the sheet cassette so that the sheet cassette is locked while the print head is pressure contacted therewith.
Further, in Japanese Patent Application Laid-Open No. 05-051137, a rotation of a motor is transmitted to a sheet feeding unit by a rotating body at the time of the sheet feeding, and a latching body is moved in an opposite direction to an urging direction of an urging member which urges the latching body by a rotational force of the rotating body at this time, and thereby the latching body is latched with a locking portion provided in a sheet cassette.
This prohibits dismounting of the sheet cassette during the sheet feeding, and prevents occurrence of the jam. Then, at the time of a non-sheet feeding when the rotating body is stopped, mounting and dismounting operations of the sheet cassette with respect to the printing apparatus main body is permitted by causing the latching body to be retracted from the latching portion by the urging force of the urging member.
In Japanese Patent Application Laid-Open No. 06-263271, in a cassette locking mechanism of a push-push type, a stopper for preventing pushing-in of the sheet cassette is provided at a portion of a lifting mechanism which lifts up a leading edge of a recording sheet stored in the sheet cassette to bring it into pressure contact with the sheet feed roller. Countermeasure is taken by causing the stopper to inhibit the pushing-in of the sheet cassette when the lifting mechanism is located at an insertion position, and to permit the pushing-in of the sheet cassette when the lifting mechanism is located at a retraction position.
Further, there is a method for energizing a solenoid and locking the movement of the cassette at a timing when one does not want to draw out the sheet cassette, and keeping it retracted at other times. In addition, there is another method for preventing the draw-out of the sheet cassette by using a dedicated actuator.
However, in the above-described locking mechanism, which is interlocked with an operation of the head or the platen during operation period of time other than when the head and the platen are pressure contacted with each other, if an attempt is made to draw out the cassette, the cassette is not locked. Therefore, the cassette can be moved in a direction in which the cassette can be drawn out.
Then, even during operation period of time other than when the head and the platen are pressure contacted with each other, the sheet is sandwiched between certain rollers. Then, when the cassette must not be drawn out, for example, when a portion of the sheet remains in the cassette, failures as described above may occur.
On the other hand, in Japanese Patent Application Laid-Open No. 05-051137, a latching body for preventing the draw-out of the cassette is directly engaged with the cassette to perform locking. In this case, the locking operation for preventing the draw-out directly acts on the cassette. For this reason, a position of the cassette may be influenced thereby, though it may be small.
Further, in Japanese Patent Application Laid-Open No. 6-263271, the stopper provided in the lifting mechanism of the sheet prevents the pushing-in of the sheet cassette. With this method, if a relationship between the stopper and the sheet cassette is set so that there is absolutely no pushing-in amount, the stopper abuts against the sheet cassette, and thereby the position of the cassette is influenced, though it may be small.
Further, a positional relationship between the stopper and the sheet cassette is set so as to permit the pushing-in to a degree that the lock is not disconnected. In this case, if the user pushes in the sheet cassette by an erroneous operation, a movement of the cassette position will be tolerated, though it may be small. As a result, the photographic printing operation may be influenced thereby.
Therefore, as discussed in Japanese Patent Application Laid-Open No. 06-263271, if a conveyance direction of the sheet and a loading direction of the sheet cassette coincide with each other, the influence is not so serious. On the contrary, if the loading direction of the sheet cassette and the conveyance direction of the sheet intersect at right angle to each other as described above, the influence may be serious.
If a position of the cassette is shifted even though it is small, by the operation that the user has tried to draw out the cassette in this way, a failure such as jamming, positional deviation, or skew may occur, depending on a configuration of the apparatus. As a result, the quality deteriorations of various photographic printing products may occur.
Further, as with a method lastly described, if an actuator is provided for dedicated use, only for preventing the draw-out of the sheet cassette during photographic printing, it may cause an increase in cost and increase in size of the printing apparatus main body.